Apparatus for cleaning and inhibiting corrosion in air preheaters and the like



April 2, 1968 AAPPARATU: FOR

6. Nov. 19, 1965 J. W KECK CLEANING AND INHIBITING 3,375,981 EROSION 2Sheets-$heet 1 mmmm J/zm M2 3??? April 2, 1968 Filed Nov. 19, 1965 J. w.KECK 3,375,981

APPARATUS FOR CLEANING AND INHIBITING CORROSION IN AIR PREHEATERS ANDTHE LIKE' 2 $heets-$heet 2 INVENTOR.

United States Patent C) 3,375,981 APPARATUS FOR CLEANING AND INHIBITINGCORROSION IN AIR PREHEATERS AND THE LIKE Julian W. Keck, 2520 SanDomingo St., Coral Gables, Fla. 33134 Filed Nov. 19, 1965, Ser. No.508,803 2 Claims. (Cl. 239-5533) ABSTRACT OF THE DISCLOSURE A device fordislodging fouling materials from the interstices of an air preheater bydischarging liquid in a flat sheet having accurately defined stablemargins is constructed as a rectangular tube having an inlet at one endand a continuous discharge slot along the bottom. The effective width ofthe slot is controlled 'by adjustably dist-ortable gates projectingalong its margins. A pair of perforated screens bridge the slot and arearched inwardly into the body in spaced relationship to each other. Theperforations in the screens turn the longitudinally flowing liquid 90and direct it downwardly through the slot, so that the downward flowthrough the slot is virtually unaffected by horizontal forces resultingfrom the velocity head in the body. The gates are protected by anchoringangle irons which project from the body in parallel relation to andfarther than the gates.

The present invention relates to apparatus for cleaning and inhibitingcorrosion in heat exchanging devices such as regenerative air preheatersof the rotary type which are used in large steam boilers to recoverwaste heat from the flue gases.

It has been known for some time that air preheaters of the cylindricalrotary type such as the well-known Ljungstriim-type preheater could beeffectively cleaned and conditioned in a manner tending to inhibitcorrosion by treating the heating surfaces with an aqueous alkalinesolution or suspension including a material such as sodium carbonate orsodium hydroxide. With apparatus heretofore available the economicadvantage of attempting to apply such processes to large preheaters ofthe indicated character has been marginal or nonexistent (depending uponvariable factors such as the character of the fuel being burned). Evenunder conditions most favorable to the use of such a process the largequantities of water and contained treatment material required in orderto effectively perform the operation have militated against this type oftreatment of preheaters having very extensive heat exchanging surfacescomposed of closely spaced fin-like portions or the like. Previousattempts to apply wash-down cleaning and treatment to such heatexchangers have involved the use of high pressure jets for dischargingthe solution or slurry. The high velocities and pressures resulted inrapid wearing of the jet orifices or nozzles and large consumptionrates. The prior arrangements have also been such that the jets had arelatively broad cross sectional contour at the points of impingementagainst the heat exchanging surfaces. Thus the slurry solution wassimultaneously directed through a large number of preheater passagesrather than concentrated in one or two, and could not be effectivelyconcentrated in any, unless very high rates were employed.

The object of the present invention is to provide an improved treatmentdevice of the indicated character which is so designed and constructedas to provide an improved narrow, sheet-like jet configuration. Afurther object is to provide an improved elongated discharge headpositioned radially in and discharging downwardly ice through the rotorof such a preheater and which delivers a graduated rate of flow from oneend to the other of the head, but which does not involve the use ofsmall jets or separate orifices and which employs relatively lowpressures in such an accurate and narrowly concentrated sheet-likedischarge as to provide improved cleaning and treatment with a reducedquantity of solution and with much less wear and deterioration of thedischarge head.

Another object is to provide improved apparatus of the indicatedcharacter having solution discharge portions which are accuratelyadjustable throughout their length and from which the discharge rate maypreset so as to vary in a desired manner per unit of linear extent ofthe discharge element.

Another object is to provide such apparatus which is of rugged andsimple construction, which does not incorporate moving parts, which isnot subject to clogging and which is readily serviceable in event anyadjustment or replacement is necessary after installation withoutremoving the preheater or boiler from service.

Other objects and advantages will become apparent upon consideration ofthe present disclosure in its entirety.

In the drawing:

FIGURE 1 is a perspective view of an upper portion of the interior of aLjungstrom-type air preheater equipped with my invention,

FIGURE 2 is a cross sectional View of the discharge element; and

FIGURE 3 is a longitudinal sectional view of the same, centrally brokenaway.

Referring now to the drawing, reference character 10 designates therotor of a Ljungstrorn-type preheater. As shown in FIGURE 1 the upperportion of the rotor is exposed within the enclosure of the preheater, aportion of the supporting framework 12 being illustrated. As is wellknown, the rotor turns slowly upon a vertical axis to carry all the heatexchanging parts of the rotor alternately from one to another of twoisolated chambers, one chamber forming a section of the flue gas ductdischarging into the stack and the other chamber forming a section ofthe air for combustion discharging into the furnace, so that the portionheated in the stack discharges its heat into the air entering throughthe air entry duct. The heat transferring portions consist of closelyspaced vertical fins which interpose a minimum resistance to verticalflow of the air and flue gases.

In order to distribute and discharge the solution in a manner which iseffective to dislodge fouling materials from air heaters of this type, Iprovide an elongated discharge head or element, generally designated 16,of rectangular cross section as best shown in FIGURE 2 and which, asbest shown in FIGURE 1, is installed in a radial position in either theflue gas chamber or in the air duct chamber of the preheater. Thedischarge element is of a length to extend across the full effectiveradial dimension of the rotor and may be attached as by hangers 14 to asuitable stationary radial supporting beam 15 so that its discharge jetportion extends horizontally above the rotor. The discharge portion ofthe element is positioned from eighteen to twenty-eight inches above therotor and discharges directly downwardly so that as the rotor turns allportions of the rotor are carried under the sheet-like discharge. Theelement is located in the down flow section, as indicated, so that thegas flow does not oppose the flow of the cleaning solution, and theelement is also angularly spaced from the position at which the rotorleaves the section, so that draining of the rotor may be completedbefore the rotor moves into the other section of the preheater.

In a preferred and successful construction, the discharge element 16 hasan internal transverse width. of 6 /4 inches.

and is approximately 3 /2 inches high. I preferably employ a waterpressure within the element which is of the order of p.s.i., butpressures as low as 3.5 p.s.i. have been successfully used. It has beenfound that a high velocity discharge from the element is not necessaryfor efficient washing of air preheaters of this nature. An importantconsideration, however, is the concentration of a large volume of liquidin the passages being washed, without permitting a low volume to enterany passages. This is not only necessary in order to wash the foreignmatter from the passages, but because, since the flue gas temperaturesin the area where the element is installed may be in the range from 300-to 800 F., a relatively low volume of liquid, if it enters some of thepassages, will tend to evaporate therefrom before the liquid isdischarged, leaving foreign matter lodged in the rotor and giving a poorflushing action. My improved element construction obtains an accuratelyconcentrated narrow band, avoiding a wide or scattered flow which wouldfeed low volume into some passages, and thereby substantially avoids theaforementioned difficulty due to substantial evaporation and deposits inthe preheater rotor from the washing solution. It will be noted that thebottom of the element is formed by two horizontally inturned flangeshaving aligned straight edges between which is a central longitudinalslot-like outlet opening 18 approximately one inch wide. A pair oflongitudinal orifice contour plates or gates, 20, 21, are provided, oneattached to each of the bottom flanges of the element and which coact todefine the slot-like discharge opening 50. Discharge slot 50 isunobstructed from end to end. Each of the gates 20, 21 includes ahorizontal top flange portion 22, a flat downturned inclined portion 24sloping inwardly toward the vertical center plane of the assembly, and aflat vertical bottom portion 25 parallel to and spaced from the centerplane. Portions 25 which cooperate to define the orifice slot 50 areadjustable toward and from one another. Screw threaded studs 28 areattached to and extend outwardly from the bottom portions of gates 20,21 at spaced intervals therealong (four-inch spacing is employed in mypreferred construction). Studs 28 extend outwardly through holes 30 inelongated angle brace members 32, 33. Each angle 'brace member consistsof a flat horizontal top portion as 34 and a vertical portion 35 whichextends downwardly slightly formed by gates 20 and 21 so as to protectthe members 20 and 21 from damage when installing or removing theelement from the air preheater. The contour plates and angle bracemembers are secured by a plurality of machine screws as 38 to the bottomflanges of the element 16. The holes in the members 20, 21, 32, 33through which the fastening screws 38 extend are larger than the shanksof the screws, so that the contour plates and their brace members can beset out of parallel, preferably with a graduatedly increasing spacingtoward the periphery of the rotor. In addition, the contour elements 20,21 are of thinner gauge material than the angle braces 32, 33 and lessstifl, so that the flanges 24 of elements 20, 21 are flexible laterallyto enable very accurate adjustment of the spacing between them. Suchadjustment by flexure of the gates is effected by means of jam nuts 40,42 on the studs 28 and engageable with opposite sides of the verticalflanges 35 of the angle brace members. It will be seen that by looseningthe inner nuts and tightening the outer ones, the gates can 'be flexedto adjust the width of the slot 5t), and vice versa. The linear velocityof the rotor, and the amount of material to be cleaned passing under theelement per unit time, are greater toward the periphery, and the slot 50is accordingly so adjusted as to be proportionately narrower toward thecenter of the preheater rotor, as indicated, and the rate of solutiondischarge is therefore graduated, throughout the length of the element,from a maximum near the periphery to a minimum at the center. The volumeof wash liquid required per square foot of heat exchanging area isgreater near the center than near the periphery of such a cylindricaldrum type preheater rotor, however, so that although the slot gates maybe adjusted for a lesser flow rate toward the center, as indicated, theactual ratio of flow rate to area is usually desirably substantiallygreater toward the center.

A pressure equalizing screen 52 is provided re-entrantly arched upwardlyinto the interior of the element 16 and overlying and enclosing an areaabove the slot 18 to provide an elongated chamber 54 extendinglengthwise above the slot 18 through which the water solution must flow.A second arched screen 55 may also be incorporated spacedly below screen52, thereby defining a second elongated chamber 58 through which thematerial must pass before reaching the discharge slot 50. Thefor-aminous screen members 52, 55 are formed of sheet metal perforatedwith holes on /8" centers, and overlie and are spaced inwardly from theslot-like discharge opening throughout the length of the assembly, andare blocked at their ends, as shown in FIGURE 3, as by end plates 57,58, so that the liquid must pass successively through the screens 52-55in order to reach the outlet. The screens are provided at their loweredges with outturned flanges clamped between the bottom flanges ofelement 16 and a perforated plate 60 which bridges the slot-like opening18 to rigidly tie and position the bottom flanges of the element. Plate60 is provided with large closely-spaced openings 62 through which theolution flows to the outlet slot 50.

Flat gaskets as 64, 65 may be interposed between plate 60 and the gates20, 21 and body 16, as shown in FIG- URE 2.

The solution inlet pipe 65 is connected to the outer end of the elementso that the liquid enters the element longitudinally and entirely abovethe screens 52, 55 which are thus interposed between the inlet and theoutlet slot. With a preheater rotor having a radial dimension ofapproximately ten feet, the discharge slot in the element 16 being ofcourse of the same length, a successful washing operation has beenobtained with the slot so adjusted as to obtain a flow rate ofapproximately 30 gallons per minute near the center of the rotor, whichis equivalent to approximately 25 gallons per square foot of areawashed, and a flow rate of 96.7 g.p.m. near the periphery of the rotor,which is equivalent to approximately 20 gallons per square foot. Withthe unit constructed and operated as shown and described, the slot widthtapers uniformly from .214 inch at the outer, peripheral end to .070inch at the inner end, and total consumption is approximately 650 g.p.m.

The arched screens 52 and 55 direct the wash liquid approaching theslot-like discharge opening of the element downwardly and substantiallyeliminate the effects of the horizontal forces resulting from thevelocity head of the liquid in the element, thereby achieving a flowwhich is a substantially true function of the static head and attaininga sharply defined sheet-like pattern. It has been found that when twoarched screens of the indicated character are employed, flow rate can beincreased or decreased as much as 50% and the pressure of the liquidsupply can be varied widely, with no measurable change in the proportionof flow volume throughout the length of the discharge slot. It is thuspossible to introduce the washing solution directly into the interior ofthe element at one end without distortion of the pattern of thedischarge due to the velocity head.

While it will be apparent that the preferred embodiment of the inventiondisclosed is well calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation and change without departing from the proper scope or fairmeaning of the subjoined claims.

What is claimed is:

1. An elongated hollow distributor element arranged to discharge liquidlaterally therefrom along its length and comprising a tubular bodyhaving an inlet at one end and a slot-like discharge opening extendingalong one side, means in the body for controlling the flow through saidopening comprising a foraminous member overlying and bridging saidopening throughout the length of the opening, and arched inwardly withinthe distributor ele ment from the opening and a second forarninousmember arched inwardly from the opening to a substantially greaterextent, said members forming serially disposed screens bridging andextending longitudinally of said opening and interposed between saidinlet and the discharge opening.

2. An elongated hollow distributor element arranged to discharge liquidlaterally therefrom along its length and comprising a tubular bodyhaving an inlet at one end and a slot-like discharge opening extendingalong one side, means in the body for controlling the flow through saidopening comprising a foraminous member overlying and bridging saidopening throughout the length of the opening, elongated angle membersdefining a pair of discharge gates extending longitudinally of andlaterally from and sealed with respect to the body on opposite sides ofsaid opening, and releasable positioning means for individuallyattaching said members to the body, said positioning means includingportions located relatively close to the gates and projecting laterallyfarther than the gates to protect the latter against unwanted mechanicaldistortion.

References Cited UNITED STATES PATENTS 647,283 4/1900 Singrum 239-451888,693 5/ 1908 Bustinza 239-5903 962,209 6/1910 Gailor 239-4511,248,565 12/ 1917 Slattery 239-597 2,029,337 2/ 1936 Parker 239-59032,779,478 1/1957 Wahlin 239-5903 3,002,700 10/1961 Mohring 239-5923,085,754 4/ 1963 Thompson 239-5903 FOREIGN PATENTS 678,901 7/ 1930Germany.

679,687 8/ 1939 Germany.

504,958 8/ 1954 Canada.

157,331 12/1956 Sweden. 1,146,612 4/ 1963 Germany.

EVERETT W. KIRBY, Primary Examiner.

